Abstract: Earth is occasionally bombarded by Ultra High-Energy Cosmic Rays beyond 10^20 eV (UHECR). This energy range is of fundamental interest because (a) there seems to be no natural accelerator mechanism which is responsible, (b) even if accelerated, UHECR should not travel cosmological distances (due to the so-called GZK cutoff), (c) but if they do travel, they are not bent by estimated magnetic fields, thereby suggesting the possibility of "Charged-Particle Astronomy" to view the Extreme Universe. Several projects aiming at their detection, such as AGASA, HiRes, Pierre-Auger and EUSO are reviewed.

Host: J. Feng